Sittel Thomas, Becker Karolin, Polly Robert, Müllich Udo, Geist Andreas, Panak Petra J
Karlsruhe Institute of Technology, Institute for Nuclear Waste Disposal, P.O. Box 3640, 76021, Karlsruhe, Germany.
Institute for Physical Chemistry, Heidelberg University, Im Neuenheimer Feld 253, 69120, Heidelberg, Germany.
Chemistry. 2025 Jul 17;31(40):e202501065. doi: 10.1002/chem.202501065. Epub 2025 May 21.
This study systematically investigates the influence of ion size on the structure and stability of complexes formed between the calix[4]arene crown ether 1,3-alt-25,27-bis(3,7- dimethyloctyl-1-oxy)calix[4]arenebenzocrown-6 (MAXCalix) and mono- and divalent ions from the alkali and alkaline earth metal series. NMR spectroscopy studies revealed that while MAXCalix efficiently coordinates large ions such as Cs, it also forms complexes with smaller ions like Na, highlighting the ligand's versatility. The size of the ion directly influences the complex structure, with two distinct structural subtypes identified via NMR and DFT calculations. In addition, π-interactions between the cation and the cation-facing benzene rings of the calix[4]arene backbone play an important role in stabilizing the complex. Larger ions like Cs benefit from π-interactions with both cation-facing rings, whereas smaller ions like K interact with only one ring, if any. These π-interactions are primarily drivers of the enhanced affinity for Cs and the resulting higher complex stability. Competitive NMR studies further confirmed that the complex stability increases with increasing ionic radius, and ions of similar size show comparable stability of their complexes.
本研究系统地研究了离子大小对杯[4]芳烃冠醚1,3-交替-25,27-双(3,7-二甲基辛基-1-氧基)杯[4]芳烃苯并冠-6(MAXCalix)与碱金属和碱土金属系列的单价和二价离子形成的配合物的结构和稳定性的影响。核磁共振光谱研究表明，虽然MAXCalix能有效地配位大离子如Cs，但它也能与小离子如Na形成配合物，突出了该配体的多功能性。离子大小直接影响配合物结构，通过核磁共振和密度泛函理论计算确定了两种不同的结构亚型。此外，阳离子与杯[4]芳烃主链中面向阳离子的苯环之间的π相互作用在稳定配合物中起重要作用。像Cs这样的大离子受益于与两个面向阳离子的环的π相互作用，而像K这样的小离子如果有相互作用的话，只与一个环相互作用。这些π相互作用主要是对Cs亲和力增强以及由此产生的更高配合物稳定性的驱动因素。竞争性核磁共振研究进一步证实，配合物稳定性随着离子半径的增加而增加，大小相似的离子显示出其配合物具有相当的稳定性。
